Gigacycle fatigue in high strength steels.

Area of Science:

• Materials Science
• Mechanical Engineering
• Fatigue Analysis

Background:

• Gigacycle fatigue in high strength steels is a critical concern.
• Internal fractures present unique challenges compared to surface fractures.
• Conventional fatigue testing is time-consuming.

Purpose of the Study:

• To review research on gigacycle fatigue in high strength steels.
• To elucidate mechanisms of internal fractures.
• To develop a predictive model for gigacycle fatigue strength.

Main Methods:

• Accelerated fatigue testing using ultrasonic fatigue testing (20 kHz).
• Investigation of unique characteristics of internal fractures (hydrogen, mean stress, size effects).
• Measurement of small internal crack growth rates using the beach mark method.

Main Results:

• Ultrasonic testing (20 kHz) proved effective for gigacycle fatigue, with negligible frequency effects for internal fractures.
• Hydrogen and size effects significantly influence internal fractures in high strength steels.
• A new crack growth law was developed, improving predictions of fatigue life curves.

Conclusions:

• Small internal crack growth is the primary driver of gigacycle fatigue failures.
• The proposed model offers more realistic predictions for high strength steel fatigue life.
• The findings are applicable to several grades of high strength steels.